Base stations and mobile stations in a mobile communication system are each provided with a filter to suppress an unnecessary wave other than a desired wave when transmitting and/or receiving a radio signal. A dielectric filter is often used for this filter.
The filter on the base station is required to reduce passband loss. Reducing passband loss requires a dielectric having a high Q value, but a reduction of passband loss using a general TE mode dielectric filter would result in an increase in size. Thus, a TM mode dielectric filter which has a lower Q value than the TE mode but can be downsized has been attracting attention in recent years (e.g., see the Citation List for PTLs 1 to 5 listed below).
For the TM mode dielectric filter, upper and lower surfaces of the dielectric need to be shielded based on the principles of the TM mode dielectric filter. For this reason, PTL 1, or the like, discloses a technique for fixing the dielectric in place while shielding the upper and lower surfaces of the dielectric.
As shown in FIG. 1, PTL 1 discloses a technique for firmly fixing dielectric resonator 2 to metal case 1 in a longitudinal direction and a vertical direction of the resonator using resonator fixing plate 3 and spacer 6. Connectors 30 are mounted on both ends of the metal case 1. It is thereby possible to provide a TM mode dielectric filter that remains stable under vibration or impact. PTL 1 corresponds to U.S. Pat. No. 6,320,484 to Furuya et al.